A gearbox assembly to couple a prime mover to a load generally requires a lubrication system for lubricating its gears and bearings with lubrication oil. For example, an aeronautical auxiliary power unit (APU) has such a gearbox that connects a prime mover in the form of a gas turbine engine to loads such as a load compressor, electric generator and hydraulic pump. A lubrication oil tank generally mounts within the gearbox housing to provide a reservoir of such lubrication oil for the gearbox lubrication system.
Loads coupled to the gearbox may have their own lubrication system. For instance, the generator connected to such a gearbox may require lubrication by means of a lubrication system using lubrication oil stored in a lubrication oil tank. When the gearbox and generator are of such design that their lubrication systems integrate together, it is usual practice to provide a single lubrication oil tank as a reservoir for both the gearbox and the generator.
When a gearbox design requires separate oil systems for the gearbox and the generator, each system with a separate oil tank but with a common oil fill port, it is difficult to insure that both tanks fill with lubrication without overfilling one tank or the other. To prevent overfill, some means must be included for periodically filling both tanks with lubrication oil simultaneously without overfilling either.
A problem with this design has been that the float valves with internal floats to perform the tank closing operations do not perform the closing operation as required. In particular, although the valve floats generally close the tanks upon filling as required, they tend to stick in the closed position after shutting, thereby interfering with refilling of the tanks. Therefore, there is a need for valves that function to seal the generator and gearbox tanks in sequence to prevent overfilling either tank and do not stick in the closed position.